Development of D–π–A Fluorescent Dyes with a 3‐Pyridyl Group as Electron‐Withdrawing Anchoring Group for Dye‐Sensitized Solar Cells

Abstract

D–π–A and (D–π–)2A fluorescent dyes (OUY‐1 and OUY‐2) with a 3‐pyridyl group as an electron‐withdrawing anchoring group have been newly developed as photosensitizers for dye‐sensitized solar cells (DSSCs). We found that both dyes OUY‐1 and OUY‐2 were adsorbed onto a TiO2 electrode through the formation of pyridinium ions and/or hydrogen bonding of the pyridyl group with the Brønsted‐acidic sites on the TiO2 surface. However, D–π–A dye NI‐6, with a 4‐pyridyl group, was predominantly adsorbed onto the TiO2 surface through coordinate bonding between the pyridyl group and the Lewis‐acidic sites on the TiO2 surface. The photovoltaic performance of DSSC based on dye OUY‐1 is comparable to that of the dye NI‐6. On the other hand, the photovoltaic performance of DSSC based on dye OUY‐2 is much lower than that of the dye OUY‐1. This work revealed that the binding mode of D–π–A dyes with pyridyl groups on the TiO2 surface can be changed by control of the basicity and electron density of pyridyl groups.

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)2A fluorescent dyes

“…The (D–π–) 2 A fluorescent dyes OUY-2 [2], OUK-2 [3–4] and OUJ-2 were prepared by Stille coupling of stannyl compound 1 [3] with 3,5-dibromopyridine, 2,6-diiodopyrazine, and 2,4-dichloro-1,3,5-triazine, respectively (Scheme 1; see Experimental section for the synthetic procedure of OUJ-2 ).…”

“…Thus, in this work, to gain insight into the photophysical and electrochemical properties of D–π–A fluorescent dyes with an azine ring as electron-withdrawing group, we have designed and synthesized the (D–π–) 2 A fluorescent dyes OUY - 2 , OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as the D–π moiety and a pyridine, pyrazine or triazine ring as the A moiety (Fig. 1), although we have already reported the synthesis of (D–π–) 2 A fluorescent dyes OUY-2 [2] and OUK-2 [3–4] and their partial photopysical and electrochemical properties. One advantage of (D–π–) 2 A fluorescent dyes over other D–π–A fluorescent dyes is their broad and intense photoabsorption spectral features.…”

Synthesis and Photophysical and Electrochemical Properties of Pyridine-, Pyrazine- and Triazine-based (D-π-)2A Fluorescent Dyes

“…Donor-acceptor-π-conjugated (D-π-A) dyes, which are constructed of the electrondonating group (D) such as a diphenyl-or dialkylamino group and the electronwithdrawing group (electron-accepting group; A) such as a nitro, cyano, and carboxyl group and a azine ring such as pyrizine, pyrazine and triazine linked by the πconjugated bridges such as oligoene and heterocycles, exhibit intense photoabsorption and fluorescence emission properties based on the intramolecular charge transfer (ICT) excitation from the D moiety to the A moiety [1][2][3][4]. D-π-A structure possess a considerable structural characteristics that the increase in the electron-donating and electron-accepting abilities of D and A moieties and the expansion of π conjugation, respectively, can lead to the decrease in the energy gap between the HOMO and LUMO because the highest occupied molecular orbital (HOMO) is localized over the π-conjugated system containing the D moiety, and the lowest unoccupied molecular orbital (LUMO) is localized over the A moiety.…”

“…Correlation of the Stokes shift (νst) and the orientation polarizability (Δf) according to eqn(1) and(2), respectively, for OUY-2, OUK-2 and OUJ-2; solvent (ε,n, Δf) : toluene (2.38, 1.4969, 0.0132), 1,4-dioxane (2.21, 1.4224, 0.0205), ethyl acetate (6.02, 1.3724, 0.199), THF (7.58, 1.4072, 0.2096) and DMF (36.71, 1.4305, 0.274) [4].In order to investigate the solid-state photophysical properties of OUY-2, OUKwe have measured the solid-state fluorescence spectra of the solids(Figure 4). The λ fl max of the as-recrystallized dyes appears at 550 nm for OUY-2, 592 nm for OUK-2, and 557 nm for OUJ-2, which shifted significantly and bathochromically by 97 nm, 112 nm, and 48 nm, respectively, compared with those in toluene.…”

“…[2], OUK-2[3] and OUJ-2 were prepared by Stille coupling of stannyl compound 1[3] with 3,5-dibromopyridine, 2,6-diiodopyrazine, and 2,4-dichloro-1,3,5-triazine, respectively, by using Pd(PPh3)4 as a catalyst in toluene at 110 ºC under an argon atmosphere (Scheme 1).Synthesis of OYJ-2:A solution of 1 [3] (0.60 g, 0.95 mmol), 2,4-dichloro-1,3,5triazine (0.071 g, 0.48 mmol), and Pd(PPh3)4 (0.18 g, 0.16 mmol) in toluene (10 mL) was stirred for 48 h at 110 ºC under an argon atmosphere. After concentrating under reduced pressure, the resulting residue was dissolved in dichloromethane and washed with water.…”